1. Field of the Invention
This invention relates generally to concrete finishing devices that provide smooth, continuous concrete surfaces of a substantially uniform grade and finish. More particularly, this invention relates to laser-operated, automatic grade controlling devices for concrete finishing of the type classified in U.S. Class 404, subclasses 84, 114, 118 and/or 120.
2. The Prior Art
As recognized by those skilled in the concrete finishing arts, after concrete is initially placed during construction, it must be appropriately finished to give it a smooth, flat, homogeneous and correctly textured surface and appearance. Numerous finishing devices, including screeds, have long been in use throughout the industry for treating plastic concrete. Known prior art systems include "bull" floats, various forms of finishing boards, strike-offs, pans, plows, blades and the like. Bull floats essentially comprise a flat wooden board attached to a handle, much like a broom handle. These floats are manipulated by a single worker. Strike-offs contact rough, unfinished plastic concrete with a rigid leading edge to initially form, level and grade.
It is well known that either external or internal vibration facilitates concrete settling and finishing, and many vibrating systems have previously been proposed. In general, vibration promotes the attainment of a smooth, uniform product. Vibration during strike-off and subsequent screeding helps to settle the concrete and eliminate entrapped air voids. Vibration helps to densify and compact the concrete. Vibrational screeding also draws out excess water thereby increasing the structural integrity of the placed concrete. A fine layer of component cement and sand aggregate is raised to the surface by vibration along with the excess water. This cementitious slurry aids subsequent fine finishing. Often screeds extend between and rest upon the forms between which the plastic concrete is actually confined. Forms constrain the concrete until it is set, and they often provide a working structural support for the typical screed or finishing machine.
The selection of strike-off design and vibration technique for a particular machine is based upon a variety of factors, such as the characteristics of the concrete. Variables relating to concrete finishing result from the selected type and percentage of aggregate, sand, cement, admixtures, and water. Temperature, slab thickness, slump and placement method also vary the application procedure. Those skilled in the art will recognize that the selected finishing equipment must be appropriately mated to the job demands.
Thus in screeding, for example, an optimum strike-off design and vibration technique must be chosen based on the condition of the concrete and the desired results. If high slump concrete is to be screeded, a floating pan would be ideal. For finishing relatively dryer concrete, a heavier twin-bladed screed or strike-off might be more desirable. In all cases it is desirable to insure the development of a proper grade. In other words, the plane of the installed concrete surface must be properly aligned and oriented.
I previously have been involved with several patents in the art of concrete placement and finishing. Typical is a prior art self-propelled "triangular truss" screed that rides upon forms seen in U.S. Pat. No. 4,349,328. Additionally, U.S. Pat. No. 4,798,494 discloses a floating vibratory screed intended to facilitate the finishing of concrete with or without forms. Finally, Allen prior U.S. Pat. Nos. 4,316,715; 4,363,618 and 4,375,351 and the various references cited and discussed therein are germane to the general technology discussed herein. The parent to the present case discloses a laser beacon directed screed control system. All the above patents have been assigned to the same assignee as the present case.
U.S. Pat. Nos. 4,650,366 and 4,386,901 disclose screeds capable of formless, self-supporting or floating operation. The latter patent speaks to a relatively heavy triangular truss screed adapted to be operated by two workmen without the use of forms. U.S. Pat. No. 4,650,366 discloses a light weight, portable vibrating screed including a central, extruded beam element. A floating screed manufactured by Les Placements Paro of Canada, although it is not necessarily prior art and is apparently unpatented, is believed relevant. It includes a floating pan that is physically offset from, and adjustably coupled to, a parallel and spaced-apart strike-off assembly.
U.S. Pat. No. 3,431,336 discloses a floating vibrating finishing screed adapted for use upon plastic concrete. U.S. Pat. No. 2,314,985 discloses a vibratory hand screed including a central, vibrated pan that is apparently adapted for use upon plastic concrete without support upon confining forms.
Another prior art floating screed of general relevance is disclosed in a video tape produced by the American Concrete Institute and The Portland Cement Association, entitled "Finishing Concrete Flatwork," that bears a Copyright date of 1984. Other prior art screeds, generally of the "form-riding" type, include those screeds disclosed in U.S. Pat. Nos. 4,340,351; 4,105,355; 2,651,980; 2,542,979; 3,095,789; 2,693,136; and 4,030,873.
Lasers are commonplace on the modern construction site. They are employed in surveying, earthwork and general layout operations. Fukukawa U.S. Pat. Nos. 4,861,189 and 4,854,769 disclose a system for paving inclined and/or curved surfaces. This system employs anchor vehicles and paving vehicles. The paving vehicles are secured to the anchor vehicles by wires. The connections of the wires to the anchor vehicles are controlled by a laser sensing device. Microcomputers control the shape of the paving devices to create compound and complex curves in paved surfaces.
Two devices employing a vehicle with a boom terminating in a screed are disclosed in Hansen U.S. Pat. No. 5,039,249 and Quenzi U.S. Pat. No. 4,930,935. Each of these patents relates to an anchor vehicle and a telescoping boom extending horizontally from the vehicle. The boom terminates in a screeding device that may also employ augers and vibrators. A second Quenzi U.S. Pat. No. 4,978,246 discloses an apparatus and method for controlling laser guided machines. This patent relates to an improvement to the above Quenzi patent.
Owens U.S. Pat. No. 4,752,156 discloses a manually operated laser guided portable screed. This invention is basically a screed with a pair of laser sensors mounted to it. Operators manually adjust the height of the screed as they draw it across placed concrete in response to a signal from the laser sensor. All of the above mentioned devices use a stationary laser beacon that projects laser light in a 360 degree plane.
However, none of the prior art devices known to us provides a satisfactorily efficient system for controlling the finished elevation of a concrete surface without the use of forms or heavy machinery. No prior art device provides for finishing plastic concrete to a uniform elevation or at a uniform angle of grade employing conventional portable, formless, floating screeds. Such screeds can be conveniently and concurrently used for vibrating, striking-off, and float finishing. Particularly, no device disclosed by the prior art is suitable for use within a building or in other confined areas. Additionally, prior art devices are restricted to a designed use and are not adaptable to a variety of uses.
The prior art devices cannot be combined to work in a gang configuration. Neither can the prior art devices be reduced to a limited number of components to facilitate use in tight spaces or to increase the efficiency of available resources. In conventional floating, vibratory screeds the relationship between the buoyancy of the pan, the plastic concrete's resultant surface tension, and the overall center of gravity of the apparatus is concurrently balanced. The prior art devices fail to take advantage of this balance.
Previously developed laser control systems for screeds employ hydraulic cylinders. In these devices, each station that monitors the remote laser beacon has a single sensor and an interconnected cylinder. There is one station at each end of the screed. Simple vertical displacements of the screed at one end can fail to adequately compensate for changes of the plane of the concrete or the underlying support strata from side to side and front to back. In other words, when grade changes are sensed, it may not be enough to simply lift or lower a screed end; the plane of the concrete may require torsional displacement of the screed to achieve the desired plane. Without such versatility, elevation compensation directed to one screed end can cause a responsive compensation in the other screed end and vice-versa. Unwanted screed oscillation or "rocking" can thus result as the opposite grade control stanchion attempts to compensate for sensed distortion. Similar front to back oscillations can also occur. As a result of the reaction and counter reaction, the screed will not smoothly assume a relatively stable, slowly changing orientation. Instead it may jerk and rock in an ineffectual fashion.
Hence, it is necessary to provide a grade control mechanism that satisfactorily controls the screed in a plane common to the resultant finished concrete, and in a plane perpendicular to the finished surface. In other words, it is desirous to not only control the elevation of the screed from end to end but also front to back (i.e., torsional control). This will allow minor adjustments at a "corner" of the screed. These adjustments should not adversely effect the opposing corner or the opposing edge of the screed. Such a device can change grade if necessary with little or no disruption of the finishing operation if the underlying surface will allow.
It is therefore desirous to provide a laser leveled screed that can independently adjust the leading and trailing edges of the screed (i.e., automatic torsional screed control). Each support tower end should be controlled by an independent laser sensing mechanism. Furthermore, it is desirous that each active side of the tower be mechanically isolated from the another so that minor torsional corrections in screed orientation do not result in oscillations.